Direct constraint on cosmic neutrino mass using observational Hubble parameter data

In order to explore the properties of cosmic neutrinos, i.e. sum of the neutrino mass (∑m_υ) and the effective number of neutrino species (N _eff), which affects the Hubble expansion rate H(z) and the power of observational Hubble parameter data (OHD) in constraining cosmological parameters under the ΛCDM model, we utilize OHD to constrain the properties of cosmic neutrinos and apply an accurate H(z) function with ∑m_υ and N _eff. First, we simulate new OHD beyond the existing 43 OHD. According to the predictions of measurements of H ₀ (the current H(z) value), baryon acoustic oscillations (BAO) peaks, Sandage-Loeb (SL) test and cosmic microwave background (CMB), we assume observational accuracy up to 2% and redshift 0 < z ≲ 5. With simulated H(z) data obtained from the fiducial model, we constrain the parameters including ∑m_υ and N _eff. When all parameters are set free, ∑m_υ < 0.196 eV (95%) and N _eff = 2.984 ± 0.826 (68%) are obtained, and when fixing N _eff as the standard baseline 3.046, we attain ∑m_υ < 0.240 eV (95%). These constrained results are much tighter than the ones obtained by the current OHD, which makes the prospect of OHD in constraining cosmological parameters more promising as its accuracy and quantity grow. (paper)